This invention concerns vibratory screening apparatus particularly for the screening of fluids such as mud obtained from well drilling operations and the like, and in particular to such apparatus having increased volumetric capacity and improved screen life. The invention further relates to a method of separating particles from a fluid in which the particles are entrained.
It is well known in the rotary drilling of wells that it is extremely important to remove drilled solids, i.e. cuttings, cavings, sand, and shale from the mud used during the drilling operation. Recirculation of the drilled solids can create viscosity and gel problems in the mud, as well as increased wear in the mud pump and mechanical equipment employed during the drilling operation. Solids control thus becomes one of the most important phases of mud control.
A shale shaker or vibrating screen has proven extremely successful in removing drilled solids from the mud. Generally, a fine screen cloth of 20 to 150 mesh is employed with the vibrating screen. The screen generally comprises at least two overlying layers of screen cloth.
The frame of the vibrating screen is resiliently suspended or mounted upon a support and is caused to vibrate by means of a vibrating mechanism, for instance a revolving unbalanced weight carried by a rapidly rotating shaft disposed transversely of the frame. Vibration of the frame caused by the vibrating mechanism results in the fine mesh screen cloth moving in an axially or longitudinal or rotational direction with respect to the frame support. Vibration of the screen serves several purposes: (1) it prevents the solids from accumulating on the screen and blocking the mesh; (2) it conveys the solids to the front of the screen where they can be collected and typically fall off to facilitate disposal; and (3) it increases the volumetric capacity of the screen.
As one would anticipate, the operating life of the fine mesh screen is extremely important. Generally, the fluid having the entrained particles or solids is delivered onto a weir or similar mechanism used for directing the flow of fluid from the source thereof onto the screen. The weir is intended to distribute the mud over a relatively large area of the screen. However, in actual practice, it has been found that the weir is generally ineffective and that a substantial portion of the mud falls on a rather limited or confined area of the screen. Further, it has been observed that a substantial portion of the mud falls from the weir downstream of the feed end or upstream portion of the screen underlying the weir. Essentially, this upstream portion of the screen is underutilized thereby reducing the overall capacity of the screen.